WAVELET ANALYSIS CONSIDERATIONS FOR EXPERIMENTAL NONSTATIONARY FLOW PHENOMENA

In this work, wavelet transforms are the analysis tools for studying transient and discontinuous phenomena associated to turbulent flows. The application in quest results from velocity measurements with hot wire anemometry in the transient wake considering a circular cylinder in an aerodynamic channel. Continuous and discrete wavelet transforms are applied and compared with the corresponding results given by the Fourier transform. For the continuous wavelet transform, the Morlet function was adopted as transform basis, and for the discrete case, the Daubechies orthonormal wavelet with 20 null moments. Results using the discrete wavelet packet transform are also presented and compared. A wake past a cylinder was analytically simulated and compared with the actual one, both in transient flow. The ability of the wavelet transforms in the analysis of unsteady phenomena and the potential of the wavelet approach as a complementary tool to the Fourier spectrum for the analysis of stationary phenomena is presented and discussed

Thermal Power Plant Boiler Misoperation -Case Study Using CFD

Abstract The actual operation condition of a thermal power plant, where the water seal in the bottom of the boiler presented an air leakage, was simulated using the commercial CFD code CFX. The results were compared with the ones for the hypothetic situation where the leakage does not exist and the total amount of air required for the combustion would be furnished by the secondary air feeds. The misoperation condition affects the performance and the flow dynamics of the boiler and also the NO x formation. * Corresponding author: [email protected] European Combustion Meeting 2009. Introduction A substantial portion of the electric energy generated worldwide comes from fossil fuel sources. In addition to economic considerations, the current concerning with greenhouse effects enhances the importance of the efforts done for a proper and efficient thermal power plant operation. Coal combustion comprises phenomena such as turbulence, radiative and convective heat transfer, particle transport and chemical reactions. The study of these coupled phenomena is a challenging issue. The state of the art in computational fluid dynamics and the availability of commercial codes encourage numeric studies of the combustion processes, as The purpose of the study is the analysis of an actual operation condition where the water seal in the bottom of the boiler presented an air leakage. The amount of air leak was evaluated by the plant staff and also computed by stoichiometric balance. The results were compared with the ones for the hypothetic situation where the leakage does not exist and the total amount of air would be furnished by the secondary air feeds

Dynamic and static task allocation for hard real-time video stream decoding on NoCs

Hard real-time (HRT) video systems require admission control decisions that rely on two factors. Firstly, schedulability analysis of the data-dependent, communicating tasks within the application need to be carried out in order to guarantee timing and predictability. Secondly, the allocation of the tasks to multi-core processing elements would generate different results in the schedulability analysis. Due to the conservative nature of the state-of-the-art schedulability analysis of tasks and message lows, and the unpredictability in the application, the system resources are often under-utilised. In this paper we propose two blocking-aware dynamic task allocation techniques that exploit application and platform characteristics, in order to increase the number of simultaneous, fully schedulable, video streams handled by the system. A novel, worst-case response time aware, search-based, static hard real-time task mapper is introduced to act as an upper-baseline to the proposed techniques. Further evaluations are carried out against existing heuristic-based dynamic mappers. Improvements to the admission rates and the system utilisation under a range of different workloads and platform sizes are explored

Multi-criteria Resource Allocation in Modal Hard Real-Time Systems

In this paper, a novel resource allocation approach dedicated to hard real-time systems with distinctive operational modes is proposed. The aim of this approach is to reduce the energy dissipation of the computing cores by either powering them off or switching them into energy-saving states while still guaranteeing to meet all timing constraints. The approach is illustrated with two industrial applications, an engine control management and an engine control unit. Moreover, the amount of data to be migrated during the mode change is minimised. Since the number of processing cores and their energy dissipation are often negatively correlated with the amount of data to be migrated during the mode change, there is some trade-off between these values, which is also analysed in this paper